Flux transfer lifting apparatus



A ril 29, 1969 s. TUBBS FLUX TRANSFER LIFTING APPARATUS I III Filed July 19,- 1966 ATTORNEY- United States Patent Office Patented Apr. 29, 1969 3,441,807 FLUX TRANSFER LIFTING APPARATU Lester G. Tubbs, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa.., a corporation of Pennsylvania Filed July 19, 1966, Ser. No. 566,350 Int. Cl. HOlh 47/12 US. Cl. 317-123 4 Claims ABSTRACT OF THE DISCLOSURE Lifting apparatus of the permanent magnet type is disclosed wherein a permanent magnet is utilized to supply a majority of its flux to either a keeper or to a magnetic load desired to be lifted. A control winding is utilized for determining which path receives the majority of flux with the direction and magnitude of the control signal provided to the control winding determining the load lifting and load dropping operation of the apparatus.

The present invention relates generally to lifting apparatus of the permanent magnet type and more particularly to a mean of controlling the operation of a permanent magnet type lifting device.

It is well known in the prior art that permanent-magnet type lifting devices are operable by control signals to effect a flux transfer in a magnetic memory device from a load end to a keeper end thereof and conversely. Since a permanent magnet exerts a relatively constant residual attractive force, a method of control is necessarily effected by switching this residual attractive force from one portion of the magnetic memory device to another portion thereof, with the flux in one instance directed through a load end including a magnetic load and in another instance through a keeper end and away from the load. This ability to switch the permanent magnet flux is typically achieved by changing the polarity of an energizing signal applied to a control winding disposed about a pole piece used in conjunction with the permanent magnet. A detailed explanation of such switching operation is discussed in US. Patent No. 3,316,514, entitled Fail Safe Lifting Apparatus by Raymond J. Radus and Lawrence R. Scott and assigned to the same asslgnee as the present invention. The energization of the control winding may be supplied by a relatively low energy battery. The magnitude of energy required is dependent upon the characteristics of the permanent magnet and the load lifting range desired.

Upon energization of the control winding with a control signal of one polarity, the majority of the flux will be transferred to the load end. Similarly, by reversing the polarity of the applied control signal, the majority of the flux will be transferred away from the load end to some other magnetic member of the apparatus, typically called a keeper plate. For safety reasons, this keeper plate is movable from a position of direct proximity to the keeper end of the magnetic memory device to a preset distance away.

Air gaps exist between the load and the lifting device on the load end and between the keeper plate and the lifting device on the other or keeper end. The magnitudes of these air gaps are varied throughout operation. For instance, when the movable keeper plate is abutting the magnetic memory device, the air gap at the keeper end is at a minimum with the magnitude of the gap dependent upon the degree of roughness of the contacting portions of the respective surfaces. On the other hand, when the keeper plate is at a maximum preset distance away from the magnetic memory device, the air gap is now largely this preset distance and the surface texture becomes incidental. But, unlike the load end where the air gap varies as the surface roughness of the load, a keeper plate air gap can be regulated and controlled since the keeper plate and magnetic memory device are a function of material, manufacture and assembly. Moreover, by appropriate protection of the keeper plate movement and operation, operating characteristics at the keeper end can be made relatively constant. This protection is generally described in US. Patent No. 3,389,358, entitled, Flux Transfer Lifting Magnet, by L. G. Tubbs and assigned to the same assignee as the present application.

Two salient limitations of permanent magnet lifting apparatus have been: (1) inadequate reduction of the attractive force at the load end to release light loads and, (2) the limited load lifting ability of permanent magnet devices as compared to electromagnets. Thus, it would be of considerable benefit to develop an apparatus for handling both light and heavy magnetic loads having both the economy and safety features associated with permanent magnet devices and the load lifting ranges comparable to an electromagnetic device.

It is, therefore, an object of the present invention to provide an improved permanent flux transfer lifting apparatus.

Another object of the present invention is to provide an improved permanent magnet lifting apparatus such ihat its operation is more capable of releasing lightweight oads.

An additional object of this invention is to provide improved permanent magnet lifting apparatus adapted to have a single power supply, and provided connecting circuitry to simultaneously operate a plurality of permanent magnet lifting devices.

A further object of this invention is to provide improved permanent magnet lifting apparatus better adapted to have the power supply and connecing circuitry detachable from the permanent magnet lifting device to permit independent movement of a load over a distance.

A still further object of this invention is to provide improved permanent magnet lifting apparatus having the electrical power supply and connecting circuitry temporarily attached to the permanent magnet lifting device to allow movement of the apparatus with or without a load over a distance.

In accordance with the present invention, portable electrical power supply and connecting circuitry are provided in an enclosure which can be attached or detached as desired from the permanent magnet lifting device itself. An improved operating range of a permanent magnet lifting device is achieved by tuning the release signal to provide maximum flux transfer at the keeper end with a corresponding minimum flux at the load end to facilitate releasing of light loads. In addition, a single electrical power supply and connecting circuitry can be better utilized to activate a plurality of permanent magnet lifting devices thereby providing additional usage of the apparatus for both large and heavy loads.

These and other objects of the present invention will become more apparent when considered in view of the following specication and drawings, in which:

FIGS. 1, 2 and 3 are illustrations of various embodi ments of the present magnetic lifting apparatus;

FIG. 4 shows the detachable signal control unit of the present invention including the electrical power supply and tuned coupling circuit;

FIGS. 5 and 6 illustrate circuitry combination that are used to optimize operation of the magnetic lifting appa ratus; and

FIG. 7 shows the fiux directions resulting from energization of the control winding of the permanent magnet lifting device.

Referring to FIG. 1, the present flux transfer lifting apparatus is shown, including a permanent magnet type lifting device and a signal control unit 12. The apparatus is subject to movement over a distance by an external hoist 14 connected to the permanent magnet lifting device 10. The signal control unit 12 is connected to the magnetic lifting device 10 by a suitable extension cord 16 which is expandible to provide remote operation as desired. The signal control unit 12 is provided with a detachable plug 18 operative with a mating receptacle on the magnetic lifting device 10. Thus, it would be possible to operate similar magnetic lifting devices with the same signal control unit. However, if it were desired to maintain a separate signal control unit for each magnetic lifting device, a handle 24 is provided which will interlock with a mating portion 26 of the magnetic lifting device 10 such that the control signal unit is carried by and moves simultaneously with the magnetic lifting device as it is carried over a distance by the external hoist 14.

FIG. 2 illustrates a simultaneous operation of two magnetic lifting devices 32 and 34 as controlled by a single signal control unit 36. A rigid-framed member 30 is suspended from an external hoist and provided with hooks to retain the two magnetic lifting devices 32 and 34 for operation to lift a common load. The signal control unit 36 is specifically designed for operation with a pair of the magnetic lifting devices as will be later described relative to FIG. 6 and is provided with two connecting cords of the type previously mentioned. This apparatus is suitable for elongated loads where lifting should be done at a minimum of two points. The signal control unit 36 is detachable from the magnetic lifting devices or may be mounted on the handles of either one of the magnetic lifting devices 32 or 34 for movement of the load over a distance.

Apparatus is shown in FIG. 3 whereby a rigid member 40 is suspended from an external hoist capable of supporting four of the magnetic lifting devices. All four units are electrically interconnected through conductors 42 and are controlled by a single signal control unit 44. This signal control unit is capable of being attached or detached from any of the illustrated magnetic devices. Similarly, it may be hung on any of the provided handles 46 for portable operation of the entire apparatus over a distance. A lift signal from the signal control unit 44 will operate all magnetic lifting devices simultaneously to provide suitable lifting forces to lift a common load. Similarly, a common release signal will operate to transfer the majority of the magnetic flux away from the load and thus release it. It should be noted that there is no theoretical limitation upon the number of magnetic lifting devices to be employed other than power supply requirements for the signal control unit 44. Should a large number of magnetic lifting devices be desired, it would be a simple matter to maintain a DC electrical power supply at each operator station which could be attached to the apparatus as required by a plug connection.

FIG. 4 illustrates a typical signal control unit whereby an operator, by activating either a lift switch 56 or release switch 58, can provide a signal from the power supply 60 and the tuned coupling circuit 62 (shown in FIG. 5) through the expandible connecting cord 64 to a magnetic lifting device connected by detachable plug 66. The signal control unit enclosure 68 has a handle 70 by which an operator can easily carry the unit. Mounted on the side of the enclosure is a hook bracket 72 which interlocks with a mating bracket mounted on a magnetic lifting device, such that the signal control unit can be carried along with the associated magnetic lifting device over a distance.

In FIG. 5 there is schematically shown the tuned coupling circuit 62 for operating a magnetic lifting device as shown in FIG. 1. The circuit is composed of the lift switch 56, a release switch 58, an adjustable resistor 24 and a power supply 60. By depressing the lift switch 56,

a signal, equal to the full energy of the power supply 60, is passed to the control winding of the magnetic memory device 80. This signal energizes a control winding in the magnetic memory device in the proper polarity for a majority of the flux to be transferred to the load end and for the apparatus to operate in a lift mode. The lift signal applies the positive side of the battery to control winding terminal 61 and the negative side to control winding terminal 63. In the same manner depressing the release switch 58 energizes the control winding of the magnetic memory device 80 to transfer a majority of the flux away from the load end to the keeper end and thereby release the load. The release signal is opposite in polarity to the lift signal, since the negative side of the battery now operates on control winding terminal 61 and the positive side of the battery operates on the control winding terminal 63. When the release switch 58 is activated, variable resistor 23 is positioned between control winding terminal 61 and the negative terminal of the power supply 60. The function of this resistor is to trim the voltage applied to the control winding of the magnetic memory device 80 such that a maximum flux transfer away from the load end is achieved in a manner to release a load. Since the purpose of each of the lift and release control signals is only to cause a flux transfer, a continued application of either the release or lift switch once the flux transfer has occurred is of no avail. The circuit referred to in FIG. 5 is especially suitable for operation of a plurality of magnetic lifting devices as shown in FIG. 3 requiring but one connecting cord to the assemblage of devices. Such operation could be achieved by parallel connecting the required plurality of control windings to control winding terminals 61 and 63 such that a common multiple operation exists. Only the power supply need be compensated in such a multiplicity of operation.

In FIG. 6 a circuit suitable for the operation of a plurality of magnetic memory devices as shown in FIG. 2 is demonstrated. This circuit includes a release switch 90, a lift switch 92, a DC power supply 94 and two variable impedances 96 and 98. Two control windings are capable of being individually energized for operating magnetic lifting devices 20 and 22 simultaneously. When the lift switch 92 is activated, voltage equal to the full power of the DC battery 94 is applied to the control windings of magnetic lifting devices 20 and 22. The negative terminal of power supply 94 is connected directly to similar control winding terminals 27 and 31 of the respective magnetic memory devices with the positive terminal of power supply 14 connected to control winding terminals 29 and 33. Upon activating the release switch 92, the positive terminal of power supply 94 is connected directly to control winding terminals 27 and 3-1 and the negative side is connected through respective variable impedances 96 and 98 to the control winding terminals 29' and 33. The variable impedances 96 and 98 may be equal or different depending upon the relative similarity in characteristics of the magnetic lifting devices 20 and 22. A circuit of this nature could be used most advantageously where the magnetic lifting apparatus consisted of two or more devices each having separate lifting and release specifications. By providing a variable impedance for each device, it would be possible to tune the respective impedances such that the operation of each magnetic memory device is individually optimized. Thus, both simultaneous operation and a high degree of efiiciency would be assured.

Referring to FIG. 7, a control winding typical of that energized by the previously described signal control unit is shown. The control winding 50 is disposed about a pole piece 52 of a magnetic lifting device. At the keeper end 53 of the structure a keeper plate 45 is positioned; at the other or load end 47 is a load 57 which can be lifted when the control winding is appropriately energized. Due to the nature of the construction of the device, two magnetic circuits are provided, one of which includes passage of the majority magnetic flux through the keeper plate 45 and the second of which includes passage of the majority flux through the load 57 abutting the load end 47. To transfer a majority of the flux to the load end 47, the control winding is energized in the direction shown by the arrow 74 to provide an induced flux in the direction shown by arrow B The intensity of this signal is such that a majority portion of the flux previously passing to the keeper plate 45 is drawn to the load end 47 and operable to lift the load. An air gap will necessarily exist between the load end 47 and any abutting load; the size of the air gap is a function of the surface roughness of the particular load. Hence, the full electrical energy of the signal control unit is used in the lift mode to energize the control winding 50 to produce maximum flux transfer to the load end 47. To release a load, the control winding is energized in the opposite direction shown by dashed arrow 76 to provide induced flux in the direction shown by dashed arrow B With the keeper plate 45 abutting the keeper end of the device, a majority of the flux which previously was acting through the load at the load end 47 is now transferred to the keeper end and operates through the keeper plate 45 such that the load is now released. To provide for more constant operation throughout its usable life, the keeper plate can be enclosed to prevent contamination from dust and magnetic particles that might otherwise hinder its movement and operation. It should be noted that with a known surface roughness of both the keeper end 53 and the keeper plate 45, the air gap between the surfaces when in contact is relatively constant. This is unlike the air gap existing between the load end and the load which varies as the surface of the load. Moreover, the air gap at the keeper end 53 is likely to be considerably less than that at the load end 47 since the surfaces of both the keeper end 53 and the keeper plate 45 are relatively smooth. Thus, it necessarily results that with a smaller air gap, the reluctance at the keeper end 53 is decreased and full energy of the electric battery is not required to transfer a majority of the flux to the keeper end. Moreover, if the full energy of the battery were employed, the keeper plate would become oversaturated and unable to handle both the magnetic flux of the permanent magnet and the induced flux resulting from the maximum energization of the control winding. That portion of the flux unable to pass through the keeper plate would spill over and develop an additional magnetic circuit which would necessarily operate at the load end 47 through the load 57. Hence, to release a load it is desirable to energize the control winding only to the extent where a maximum attractive force operates at the keeper end with no flux spill over to the load end. The determination of this magnitude of energization to the control winding will also determine the lightest load that can be released by the magnetic device. A practical method of determining the lightest load that can be released is to place a test load at the load end 47 with the magnetic device operating in its lift mode. The device can then be energized to its release mode with full strength of the electrical supply. If release of the load is not achieved, a portion of the electrical energy can be trimmed off by the adjustable resistors 25 in FIG. 5 and 96 and 98 in FIG. 6. By adjusting these impedances until the load is released, an optimum signal for energizing the control winding 50 to transfer a majority of the magnetic flux through the keeper plate 45 and cause a minimum attractive force at the load end 47 can be attained. This procedure will effectively determine the minimum operating range of the device.

Use of this apparatus would usually be in conjunction with an external hoist. The external hoist would position the apparatus over a load and lower the lifting apparatus such that the load end of the magnetic lifting device was abutting the load. Then a momentary application of the lift control signal would cause the majority of the magnetic flux to operate through the load end and its abutting load such that when the external hoist lifted the lifting apparatus the load also was lifted. Since only a relatively small electrical supply energy is required, the signal control unit can be mounted directly on the magnetic lifting device and travel with it as the load is carried over a distance by the external hoist. When the load is to be released, the external hoist will position the lifting apparatus and the load such that the load is resting on a support surface. Then the operator can lift off the signal control unit, if it were carried along with the apparatus, and momentarily apply a release signal until the load is to be released. The external hoist may now lift the magnetic lifting apparatus away from the load. If only a single magnetic lifting device is involved, it would be quite likely that the signal control unit, being lightweight and inexpensive, would be carried along with the magnetic lifting device throughout its operation. However, if a plurality of lifting devices is used, it might be preferable that the signal control unit would remain at the operators station and use could be made of one or more detachable connecting cords which could be operative with the magnetic lifting devices.

A practical embodiment of the described apparatus as shown in FIGS. 1 and 5 was actually built and operated having the following operational values:

Permanent magnet strength Permanent magnet force 10,000 oersteds; retentivity 3950 gauss; coercive force 2200 oersteds.

Battery 60 9 volts.

Resistor 23 7.5 ohms.

Control winding 720 turns of #17045 wire; 5.75 ohms at 25 C.

Rated operating range 15 to 1500 pounds.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made by way of example and that numerous changes in details of construction and combination and arrangement of parts and elements may be resorted to without departing from the scope and spirit of the present invention.

I claim in my invention: 1. In lifting apparatus of the permanent magnetic type for lifting a magnetic load, the combination of:

permanent magnet lifting means having a keeper end and a load end at the opposite ends thereof and including a permanent magnet having one end disposed adjacent said load end, a keeper member disposed adjacent the other end of said magnet at said keeper end, and a control winding for determining the magnetic circuit path of the majority of the magnetic flux supplied by said permanent magnet through either said keeper or said load end of said permanent magnet lifting means; power supply means for providing a first and a second control signal to said control winding, said first control signal having a first direction and a first magnitude, and said second control signal having a second direction and a second magnitude, with said first direction being opposite to said second direction and with said first magnitude being different from said second magnitude; and circuit means for connecting said power supply means to energize said control winding of said magnet lifting means so that said first control signal controls the lifting of said load and said second control signal controls the release of said load. 2. A lifting apparatus as set forth in claim 1 wherein: said circuit means includes a variable impedance which can be adjusted to energize the control winding to provide a substantially maximum flux strength to the load with the lifting apparatus having been energized operable with said permanent magnet lifting means by said first control signal and a substantially minithrough detachable connecting means. mum flux strength to the load when said apparatus has been energized by said second control signal. References Clted 13 liftigg apparatus for magnetic loads as set forth in 5 UNIT D STATES PATENTS said circuit means is calibrated to energize said control gii 'g Winding to transfer substantially maximum flux 1915f566 6/1933 Yomgl ggg 317 123 strength to the load end of said apparatus in re- 1737846 12/1929 Hod E sponse to said first control signal and to transfer 10 6/1910 Eastgvood 317 123 substantially maximum flux strength to a keeper end of said apparatus in response to said second control JOHN F. COUCH, Primary Examincl.

signal. 4. A lifting apparatus for magnetic loads as set forth TRAMMELL Assistant Examum' in claim 3 wherein: 15 US. Cl. X.R.

said power supply means and said circuit means are 335-291 

